1. Field of the Invention
The present invention relates to semiconductor memory devices, and more particularly to an expansible FIFO (first in first out) semiconductor memory device to which additional memory stages having the same internal memory structure may be connected to form a multistage memory of increased memory storage capacity.
2. Description of the Prior Art
For large scale general-purpose computers, the amount of data to be processed has continued to increase through the years. From the viewpoint of access time, throughput and required memory capacity consistent with the ever-increasing volume of data to be processed, the use of an expanded memory storage device between a main memory storage device and a magnetic disk storage device has been a possibility. The function of the expanded memory storage device would be to fill the access time gap between the main memory storage device and the magnetic disk storage device, and also to provide a memory storage capacity larger than that of the main memory storage device, and capable of sequential access.
Heretofore, memories truly appropriate for such a purpose have not existed in the market. Consequently, DRAMS (dynamic random access memories) have been used for this purpose in the prior art. However, when the memory employed as an expanded memory storage device is a DRAM, device control is complicated and a control circuit for performing necessary control functions tends to have a large number of circuit components. The increase in the memory capacity provided by a DRAM when serving in the role of an expanded memory storage device is responsible for the change in the control circuit adding significantly to the complexity thereof, and thus the memory capacity can not be easily increased.